1. Field of the Invention
The present invention relates to a lens apparatus, particularly to one which is used as a projection lens apparatus for a liquid crystal projector.
2. Description of the Related Art
Japanese Patent Application Publication Nos. 8-304739 and 10-171045 disclose a liquid crystal projector in which a light source illuminates three liquid crystal panels for red (R) light, green (G) light and blue (B) light, respectively, on which an image is displayed, and the R, G and B light of the image that has passed through the three liquid crystal panels is combined through a cross dichroic prism, then the composed light of the image is projected on a screen through a projection lens apparatus.
The lens apparatus which is used as the projection lens apparatus comprises a zoom lens, a focus lens and a fixed cylinder supporting the lenses, and has a zoom ring and a focus ring. The zoom ring is rotatably arranged on the fixed cylinder, and the focus ring is arranged to be movable back and forth on the fixed cylinder. Rotating the zoom ring causes the zoom lens to move back and forth along the optical axis, whereby the zoom is adjusted. Moving the focus ring back and forth causes the focus lens to move back and forth along the optical axis, whereby the focus is adjusted.
In recent years, the liquid crystal projector has been miniaturized, and the projector can be carried with a lap-top computer. Many of the miniaturized liquid crystal projectors are not equipped with an electric mechanism for the focus and zoom adjustments, and the focus and zoom adjustments are performed by manual operations.
The majority of the lens apparatuses for the liquid crystal projector are of a type commonly called a front lens focusing. The miniaturized liquid crystal projector uses a collapsing type lens apparatus with a collapsing mechanism in order to be small-sized. The conventional collapsing mechanism is interlocked with the zoom mechanism, and collapsing is achieved by moving the zoom ring.
However, because the focus lens is arranged in front of the zoom lens in the lens apparatus, the zoom ring is arranged closer to the body of the liquid crystal projector than the focus ring; for that reason, when collapsing is performed by operating the zoom ring, the focus ring can not collapse completely and it still protrudes from the body of the liquid crystal projector.
The present invention has been developed in view of the above-described circumstances, and has as its object the provision of a lens apparatus which is capable of collapsing the focus ring completely.
In order to achieve the above-described object, the present invention is directed to a lens apparatus, comprising: a fixed cylinder of which axis is identical with an optical axis of the lens apparatus; a zoom lens arranged in the fixed cylinder movably along the optical axis; a focus lens arranged in the fixed cylinder movably along the optical axis; a zoom ring which is rotatably arranged on the fixed cylinder, the zoom ring being rotated to move the zoom lens along the optical axis to adjust zoom of the lens apparatus; a focus ring which is arranged on the fixed cylinder movably along the optical axis, the focus ring being moved to move the focus lens along the optical axis to adjust focus of the lens apparatus; and a collapsing mechanism which, when the focus ring is moved back over a range of movement for adjusting the focus, connects the focus ring to the zoom ring and rotates the zoom ring along with the back movement of the focus ring so as to move the zoom lens back over a range of movement for adjusting the zoom.
The lens apparatus of the present invention is provided with the collapsing mechanism which achieves collapsing by moving the focus ring; thus, the focus ring is collapsed in the body of an apparatus such as a liquid crystal projector when the focus ring is moved which is positioned at the front of the zoom ring along the optical axis. According to the collapsing mechanism, the focus ring is connected to the zoom ring when the focus ring is moved back over the range of movement for adjusting the focus, and the zoom ring is rotated when the focus ring is moved to the back, whereby the zoom lens is moved back over the range for adjusting the zoom. Since a movable range of the focus lens at a time of collapsing can be obtained by moving the zoom lens to the back, a movable range of the focus ring at a time of collapsing can be deep. Therefore, the focus ring can be collapsed completely in the body of the apparatus.